International civil servants - including 10,000 Washington-area employees of world organizations - now may sue their employer if they believe they have been ilegally or improperly fired.

A decision by U.S. District Court Judge Aubrey E. Robinson Jr., says that groups like the United Nations, World Bank and Organization of American States are not protected from employee lawsuits either by diplomatic or sovereign immunity. In the past international bodies have argued that they cannot be sued because of diplomatic immunity which they believed applied to such cases as employe charges of alleged breach of contract.

Robinson's decision, which has jolted top management of international organizations, come in the case of 7 former OAS employees. They had sued the OAS on grounds that their dismissals in August 1976 were improper, and a denial of "acquired rights." The OAS made a staff cutback of about 60 persons about that time. Seven senior workers, five Americans, Haitian and Peruvian national, sued.

The case of the dismissed employees was taken up by the administratvie tribunal of the OAS. It ordered the employes reinstated. Under the OAS charter, the socially-prominent Secretary General Alejandro Orfila could and did refuse to reinstate the workers. Instead they were offered a settlement or serverance that amounted to about 6 months pay for each employe.

Employes of many international organizations enjoy some of the world's top civil service salaries and benefits. Their federal and local taxes are paid by their employer. The seven dismisses OAS workers sued in U.S. District Court asking for a settlement of about $2.5 million that includes, they said, lost benefits and loss of future income until age 65 when they would have been eligible to retire. The OAS moved to have the suit dismissed on grounds it cannot be sued in such cases.

Robinson's brief decision, which did not touch on the financial claim of the ex-OAS employes, said the "immunity which defendants enjoy is not an absolute immunity . . ." in cases of employment contracts.

The Organization of American States said it would have no comment on the judge's decision or the case itself. The next step is for the case to go to trial in the U.S. District Court.

State Department officials said they were "very interested" in the decision but would have to comment on it. Some observors feel that State is in a diplomatic bind. On the one hand it is interested in the world groups and in defending U.S. citizen employes. On the other it is bound, as in the case of the OAS charter, to observe the prohibition against member nations interfering in internal personnel matters. Some employes say that not all nations abide by the hands-off attitude in staff placements, promotions and firings.

World-wide, an estimated 50,000 Americans work in the international civil service. American taxpayers now supply 66 cents of every dollar given to the OAS, which has a budget of $82 million. The Carter administration wants to cut that down to 49 percent, and have the other 23 member states and observors pay more.

Unless the OAS appeals the District Court ruling, other international organizations expect to be hit by lawsuits - from Americans and employes of other nations - claiming they have been manhandled by their bosses.